This proposal will study the effects of delivery and overexpression of three distinct genes, separately as well as in combination, upon the healing of articular cartilage lesions in vivo. Damage to articular cartilage represents a major problem in acute joint trauma, as well as being a major contributor to the pain and dysfunction associated with osteoarthritis (OA), the leading cause of disability in this country. Unfortunately, injured adult hyaline articular cartilage does not heal effectively on its own. Cartilage is formed by cells called chondrocytes that surround themselves with a dense extracellular matrix, composed primarily of type 11 collagen, glycosaininoglycans and proteoglycans. But adult chondrocytes retain only a limited capacity for proliferation and new matrix synthesis. In recent years, considerable progress has been made in the identification of growth factors that can augment normal cartilage reparative activities, by enhancing chondrocyte proliferation as well as the rate of new matrix synthesis. In theory, such growth factors might improve the healing of cartilage defects. Unfortunately, the clinical application of these polypeptide growth factors to articular cartilage defects has been seriously complicated by their short pharmacological half-lives. Strategies of direct delivery of these potent but short-lived proteins are clearly not ideal. By contrast, the delivery of gene cassettes encoding these factors offers the potential of long-term benefits from a single or small number of treatments. A major obstacle to a gene based approach to treating injured cartilage has been difficulties in introducing foreign DNA into the cartilage, likely due in part to the dense extracellular matrix surrounding the chondrocytes. We believe recombinant vectors derived from Adeno Associated Virus (rAAV), with which our lab has considerable experience, are ideally suited to this purpose. Recent findings from our group and others demonstrate that rAAV can be a powerful tool to efficiently and persistently transduce chondrocytes in vitro as well as in articular cartilage in vivo. We propose to use this vector system to deliver gene sequences for two distinct chondrocyte growth factors, IGF-1 and FGF-2, directly into the knee joint in a rabbit model of articular cartilage injury as a direct test of this concept. In addition to being strong individual candidates, these two factors appear to function by different mechanisms of action, so they may reinforce each other's effects or act synergistically. We will further complement our strategy by also delivering IGF-I together with its receptor. In this way, we may enhance the action of the factor and prevent downregulation of native IGF-I receptors following prolonged overexpression of IGF-1. We believe this proposal combines the best of the state of the art with respect to both the gene candidates being delivered and the delivery system itself, in a pilot evaluation of a highly promising and novel approach to this important problem. We believe these studies have a high probability of success, and hope this project will establish the foundation for a clinically relevant, gene-based approach to healing injured articular cartilage.